Personnel in the vicinity of these machines are exposed to high noise levels, exceeding 105 dB(A), which cause physiological disorders and in particular deafness.
It is known that the main sources of noise are the air exhaust, the drill bit and the drill body. The total sound energy emitted by the drill mechanism (ie. by the drill body and by the air exhaust) varies from 35% to 90% of the total overall radiated energy, depending on whether the drill is a heavy drill or a light drill and on whether the drill bit is of small or large cross section. It is thus particularly important to reduce the noise emitted by the drill mechanism.
Proposals have already been made, in particular in an article entitled "Noise Control of Jumbo-Mounted Percussive Drills" which appeared in the journal "NOISE CONTROL ENGINEERING", volume 15, No. 3, November-December 1980, to enclose the drill mechanism in a casing of heavy gauge sheet metal (1/4" to 3/8"thick) which is easy to open and which has its inside surface covered in acoustically insulating material (in particular glass wool) which is held in place by a perforated plate. According to this document, neither the casing, nor the insulating material, nor the perforated retaining plate are in contact with the drill mechanism. It is essential to avoid contact as much as possible between the casing and the drill. The drill touches the casing only via its base plate. There is thus an empty interior volume between the drill and the casing, over the entire length thereof. The front wall of the casing has an opening to allow the air coming from the drill mechanism exhaust orifice to be evacuated to the atmosphere. Air flows freely between the orifice and the opening through which it escapes to free air.
Preferred embodiments of the present invention provide a sound-proofing casing for a pneumatic drill, which casing is designed to improve effectiveness from the point of view of reducing the noise due to the air exhaust.